I circumvented this problem using sim launcher (skips the start menu entirely) to utilize fsx. When I quit fsx, I just hit ctrl+c and it will immediately close fsx without any errors. Other way to quit would be using 'end flight' but that's pointless because it will return to fsx default menu. Sim launcher can load a flight while fsx is running so it's got you covered, preventing the need for using the startup menu AT ALL.

PS, since I do not exit fsx through the startup menu, it's then possible to narrow the crashing scenario to exiting fsx through the menu after ending a flight with the an-2. I use SL for many months now and used the an-2 quite a lot of times to prove this method is indeed crash-proof.

PS #2, using SL, you can turn Off "disable preload" as it's not effective anyway. SL will launch straight into flight while "disable preload" is merely for booting fsx startup screen faster.

I hope you find this little piece of advice useful. I do expect a proper solution though.